1. Field of the Invention
The present invention relates to a drive structure useable with a lawn and garden tractor that carries and powers an implement such as a rotary mower.
2. Description of the Related Art
Many vehicles, such as lawn and garden tractors, are adapted to carry and operate a variety of implements such as rotary lawn mowers. It is common for these types of implements to be carried beneath the chassis of the vehicle and to be adapted for up and down adjustment throughout a range of operation. More specifically, belly-mounted implements, such as rotary grass mowers, can typically be adjusted to provide for a desired height of cut. To drive the blade or blades of a rotary mower, a pulley and belt arrangement is commonly provided beneath the vehicle chassis, with the engine generally carried above the chassis, and the crankshaft projecting through the chassis. Coupled with the engine crankshaft is a pulley around which is entrained a V-belt that is also entrained around the pulley or pulleys carried on the spindle or spindles of the mower implement.
Since the pulley carried by the engine crankshaft cannot easily be raised and/or lowered due to the fact the engine is bolted to the vehicle chassis and since the implement must be raised and/or lowered for different heights of cut, the angle at which the drive belt moves into and out of the drive pulley, as well as the driven pulleys, will vary with the adjusted height of the implement. Accordingly, excessive angles of entry and/or exit of the belt into and out of the pulleys can cause excessive belt wear on and/or premature failure of the belt.
Because it is desirable to minimize these angles of entry and exit, jacksheave arrangements have been used to vertically step the power downwardly. A jacksheave typically includes a vertical shaft rotatably coupled with two vertically spaced pulleys, the top pulley being driven by a belt powered by the crankshaft and the botton pulley in turn being used for driving the implement pulley. A second belt is mounted around the lower pulley carried on the jacksheave to drive the spindle and/or spindles of the mower. Through this stepped power transmission, the lower pulley of the jacksheave arrangement is provided closer to the horizontal plane at which the mower blade pulleys on the implement operate. Such an arrangement obviously requires additional pulleys, shafts, and belts and presents increased maintenance problems and costs due to the extra parts. Further, it may restrict the vertical adjustability of the implement beneath the chassis.
To minimize the number of parts required, improve the implement vertical adjustment range, and keep the angles of entry and/or exit of the belt into the various pulleys within an acceptable, narrower range of operation, it would be desirable to provide a belt implement drive structure wherein a single belt could be used between the engine and implement without the use of a jacksheave arrangement.